December/January 2022

BY Damien Coleman, Product Manager/ EBI Specialist at Snap-on T his Toyota Prius had malfunction warning lights illuminated and two faults relating to the High Voltage System stored: Module Code Hybrid control module P3000 battery control system HV battery control module P0AFA hybrid battery system voltage low Intermittently, the vehicle would not enter ‘ready mode’. As a result, the high voltage system would remain inactive as the high voltage contactors, namely system main relay (SMR) 1, 2 and 3, were not being switched on by the high voltage control module. The system has three SMRs: SMR 1 : Positive contactor SMR 2 : Pre-charge contactor SMR 3: Negative contactor The pre-charge function is to limit the initial supply of current from the high voltage battery to the inverter. Please refer to Fig.1. Sequence of operation of SMRs: 32 AFTERMARKET DECEMBER/JANUARY 2022 TECHNICAL/SNAP-ON www.aftermarketonline.net TOYOTA PRIUS: HIGH VOLTAGE SYSTEM FAULT With EVs and hybrids continuing to grab the headlines, Damien takes a timely look at a problematic Toyota Prius Ready on SMR 1 Stage 1 Stage 2 Stage 3 Stage 4 Off Off On On Off On On Off SMR 1 SMR 1 Off On On On High voltage system off SMR 1 Stage 1 Stage 2 Stage 3 On Off Off Off Off Off SMR 1 SMR 1 On On Off Live data As the high voltage battery is located in the luggage compartment and access is difficult, live data was used to monitor the battery voltage for each battery block. The high voltage battery is made up of 14 x 14.4V blocks. Each block is made up of 2 x 7.2V cells. This equates to a total voltage of 201.6 volts. Anything over 60 volts direct current (DC) is considered high voltage. This means precautions must be taken when working on such a vehicle. This includes appropriate training, PPE, insulated tooling, etc. It must be noted that the high voltage system must only be worked on by suitably qualified technicians. The high voltage service plug must be removed and the system allowed adequate time to de-energise prior to carrying out work on the system. Please refer to Fig.2, where the arrow shows the high voltage service plug. Each battery block has a sensing wire attached to a negative stud which is wired to the high voltage control module. Please refer to Fig.3, which shows three blocks as an example. 1) High voltage battery control module 2) High voltage cable. 3) Cell (negative connection) 4) Cell (positive Connection) 5) Battery bus bar A) Battery block 1 sensing wire B) Battery block 2 sensing wire C) Battery block 3 sensing wire Please now refer to Fig.4, which shows a high voltage battery control module and current clamp (white component) on negative wire. Erratic Next, refer to Fig.5, which shows the data observed for four of the fourteen battery blocks. The first two graphs can be seen to be erratic and not behaving like the other two. The voltage had an irregular cycle between 16 volts negative and 15 volts positive. This condition is not possible, so further investigation was required, which required disassembly of the battery casing. The bus bars connecting the battery cells were found to be corroded, so they were removed and cleaned. Please refer to Fig.6. The wiring and connections associated with the battery block sensing circuits were also inspected and cleaned. However, the fault was found to still be present once the system was reassembled and powered up. Next, the connections on the high voltage battery control module were inspected. It was noted that three of the pins on the module were badly corroded. See Fig.7. This module was replaced and the fault codes cleared. The live data now